Cattle Sales: What Tests to Perform?
Livestock Update, November 2000
W. Dee Whittier, DVM,
Extension Veterinarian, Cattle,
Department of Large Animal Clinical Sciences
Virginia-Maryland Regional College of Veterinary Medicine, Virginia Tech
For a number of years testing cattle for certain diseases as they are sold has been an effective way of preventing introduction of diseases into previously clean herds and monitoring diseases in general. Changes in the diseases for which tests are performed are now being discussed and implemented as a result of disease control status and incidence changes.
Historically the diseases that have received most attention for sale testing have been the regulatory diseases: those that are regulated by state and federal laws. Often these diseases are ones that threaten human health as well as animal health. For cattle the major priorities have been Brucellosis or Bangs disease and Tuberculosis.
A significant amount of progress has been made in the eradication of Brucellosis in the United States. Only a handful of known infected herds now remain and surveillance suggests little possibility of unknown infected cattle herds. Experts suggest that the entire US cattle herd may be declared free of Brucellosis in the next couple of years. Of course some surveillance will remain to be absolutely certain that no infected cattle have been missed and because reintroduction of Brucellosis into the cattle herd from infected wildlife or from foreign countries is always a possibility.
Tuberculosis eradication has likewise enjoyed considerable success. Eradicating the last elements of TB from the US will probably be a greater challenge than for Brucellosis since uncovered pockets of infection, introductions to cattle herds from wildlife or farmed deer, and introductions from Mexico have continued.
In general producers selling cattle for breeding purposes should see less requirement for Brucellosis and TB testing of cattle at sales. There is no legal requirement for testing for either of these when cattle are sold within the state currently, except for livestock market surveillance programs. However, many states still require testing of breeding or exhibition cattle entering their states. As other states have more confidence in the status of national eradication interstate testing requirements should be decreased. The repeal of current regulations in other states will come slowly, however, even after national eradication has occurred.
Testing for diseases whose major threat is to cattle is becoming more common for breeding cattle sales. The major diseases that are considered for testing include anaplasmosis, leukosis and Johne's disease.
Anaplasmosis is a disease that attacks the red blood cells of cattle. The disease is often spread by ticks and exists in certain areas in Virginia where the ticks that can transmit the disease spread it among cattle. When cattle are infected early in life they become lifetime carriers unless treated but never show any symptoms of the disease. Only when older cattle are infected does serious disease or death result. Since most young cattle in these infected areas become infected there is little disease seen in these areas. However, if these cattle are moved into other herds that have not contracted anaplasmosis they pose a threat to their herdmates. In these new herds the disease can be spread by the transmission of tiny amounts of blood even if the ticks are not present. This may occur by as simple a procedure as using a common needle to inject infected, then noninfected cattle. Testing cattle that are being sold for breeding purposes can prevent the introduction of anaplasmosis carrier cattle into noninfected herds.
Leukosis is a disease caused by a virus (BLV). The outright form of the disease is relatively rare but is a cancer disease that always results in death. The disease occurs in only a very small percentage of cattle that are infected with the virus. A 1997 survey of cattle in the US estimated that 51% of all beef operations in the southeast and 17 % of all beef cattle are infected with the virus. A debate persists as to whether it is worth the cost of eliminating all cattle that carry the BLV virus to avoid the rather small losses that occur from the disease. In general the decision has been that the costs of eradication outweigh the potential benefits. Some herd owners have initiated eradication efforts independently in their own herds. Probably the most significant impact of the disease is for elite purebred producers who are involved in exportation of cattle genetics as some foreign countries prohibit importation of infected cattle, semen or embryos. Some very elite sales may choose to require cattle selling to test negative for BLV but generalized testing for the disease is probably not warranted.
Johne's disease is a disease that causes significant losses to the cattle industry. The disease results in a diarrhea that causes weight loss and eventually results in death. There is some concern that the bacteria involved may be a partial cause of Crohn's disease in people. The problem with testing for this disease is that it nature makes accurate testing very difficult. Experts agree that herd based programs are the best way to certify that cattle being sold are not infected with Johne's disease. These herd-based programs require that an owner test large numbers of cattle on the farm and implement other control measures to assure that infected cattle do not exist on the farm. To date these programs have not been initiated in Virginia.
A testing program for disease when cattle are being sold should be tailored to the nature of the cattle and sale. If tests are chosen wisely they can help sellers maintain reputations for healthy cattle and buyers assure that they do not bring important diseases into their herds when they purchase herd additions.